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From Apache Wiki <wikidi...@apache.org>
Subject [Pig Wiki] Update of "PigExecutionModel" by Shravan Narayanamurthy
Date Wed, 30 Jan 2008 01:36:44 GMT
Dear Wiki user,

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The following page has been changed by Shravan Narayanamurthy:
http://wiki.apache.org/pig/PigExecutionModel

------------------------------------------------------------------------------
  
  attachment:FILTERTranslation.png
  
+ === Comments ===
+ 
+ The Physical plan and the Logical Plan were not clear to me probably because of the nested
query plan thingy. I think we need to find a better way to draw this because, the conditional
expression is an attribute of the filter and not an input to filter.
+ 
+ 
  __GROUP__
  
  The logical operator co-group would be converted to 3 physical operators the Local Rearrange,
Global Rearrange and Package as shown below:
@@ -177, +182 @@

  
  The Package just takes each key, list of values and puts it in appropriate format as required
by the co-group. So lets say we have (1,R),(2,G) in A and (1,B), (2,Y) in B. If there are
two reducers, Global Rearrange catering to reducer 1 will have {1,{(1,R),(1,B)}} as the key,
list of values which should be converted into an output tuple for co-group based on the tagged
index of the tuples in the list. So this would be converted to {1,{(1,R)},{(1,B)}}. Similarly,
{2,{(2,G),(2,Y)}} will be converted to {2,{(2,G)},{(2,Y)}} by reducer 2.
  
- === Comments ===
- 
- The Physical plan and the Logical Plan were not clear to me probably because of the nested
query plan thingy. I think we need to find a better way to draw this because, the conditional
expression is an attribute of the filter and not an input to filter.
- 

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